Analyzing an enabled loop

To determine if the stand-alone dump was requested because of an enabled loop, you need to view the system trace table. Repetitive patterns in the system trace table indicate an enabled loop condition. An enabled loop, however, does not normally cause a system outage. It will cause an outage in these circumstances:

There is a non-preemptable loop in SRB mode
There is a loop in a high priority address space that is in TCB mode

In Figure 1, the CLKC entries indicate an enabled loop, and because column three is all zeroes, this loop is in SRB mode. The PSW addresses on the CLKCs identify the looping program. Use the WHERE subcommand to locate the responsible program.

Figure 1. Example: SYSTRACE output (recognizing an enabled loop)

01 003E 00000000   CLKC      070C0000 8100765C  00001004 00000000
01 003E 00000000   CLKC      070C2000 81005638  00001004 00000000
01 003E 00000000   CLKC      070C0000 810056E6  00001004 00000000

01 003E 00000000   CLKC      070C0000 80FF0768  00001004 00000000

01 003E 00000000   CLKC      070C0000 80FE4E34  00001004 00000000

01 003E 00000000   CLKC      070C1000 81004BB8  00001004 00000000

Because of interrupt processing that occurs during an enabled loop, the stored status data might not point to the module causing the loop. To determine if a first level interrupt handler (FLIH) was active, view the PSASUPER field of the PSA. If the PSASUPER field is non-zero, a FLIH was active at the time of the error. Using the FLIH's save area, find the PSW and registers at the time of the error. The address in the second half of the PSW will point to the module involved in the loop. See Problem data saved by first level interrupt handlers for more information.